Variable displacement vane pump

ABSTRACT

A variable displacement vane pump includes a pump housing, a drive shaft supported in the pump housing, a rotor rotated by the drive shaft, a plurality of vanes mounted to the rotor, a cam ring disposed movably around the pump element and a pressure plate arranged facing the rotor and the cam ring. The pressure plate has formed therein a discharge hole and a drive shaft insertion hole. The pump housing has formed therein a suction hole, a high-pressure chamber and a low-pressure chamber. The variable displacement vane pump further includes a first seal member disposed on a pressure receiving surface of the pressure plate so as to separate the drive shaft insertion hole from the high-pressure chamber and a second seal member disposed on the pressure receiving surface of the pressure plate so as to separate the low-pressure chamber from the high-pressure chamber and the drive shaft insertion hole.

BACKGROUND OF THE INVENTION

The present invention relates to a variable displacement vane pump for use as a hydraulic pressure source in an automatic transmission of a vehicle etc.

Japanese Laid-Open Patent Publication No. 2012-163040 discloses a conventional type of variable displacement vane pump for use in an automatic transmission of a vehicle. This variable displacement vane pump includes a cylindrical pump housing provided with a pump element storage part, a drive shaft inserted and supported in the pump housing, a pump element placed in the pump element storage part and having a rotor rotated by the drive shaft and a plurality of vanes attached retractably to an outer circumferential portion of the rotor and a cam ring disposed around the rotor and movable eccentrically relative to the drive shaft. There are a plurality of pump chambers defined in a circumferential direction by the cam ring, the rotor and the vanes. The discharge flow rate of the variable displacement vane pump can be varied by changing the volumes of the respective pump chambers according to the amount of eccentricity of the cam ring.

SUMMARY OF THE INVENTION

The variable displacement vane pump is immersed in a hydraulic fluid when mounted to the inside of the automatic transmission so that, whereas the high-pressure chamber side of the variable displacement vane pump is separated fluid-tightly, the low-pressure chamber side of the variable displacement vane pump is in fluid communication with a bearing part of the pump housing via an axial clearance between the pump housing and the rotor so as to allow leakage of the hydraulic fluid to the outside of the pump housing. In such a fluid communication structure, there is a problem that the hydraulic fluid in the bearing part of the pump housing is sucked up, or the outside air is sucked in, under the generation of a negative pressure with increase in the volumes of the pump chambers by rotation of the rotor during fluid suction operation. This suction problem results in e.g. sliding wear of the drive shaft due to poor bearing lubrication of the drive shaft.

In view of the foregoing, it is an object of the present invention to provide a variable displacement vane pump capable of preventing a drive shaft from poor lubrication by solving the above-mentioned suction problem.

According to one aspect of the present invention, there is provided a variable displacement vane pump for supplying a hydraulic fluid from a fluid reservoir, comprising:

a pump housing provided with a pump element storage part;

a drive shaft supported rotatably in the pump housing;

a pump element placed in the pump element storage part, the pump element comprising: a rotor rotated by the drive shaft and having a plurality of slots formed therein at positions in a circumferential direction around a rotation axis of the rotor; and a plurality of vanes retractably mounted in the respective slots;

an annular cam ring disposed movably around the pump element in the pump element storage part, thereby defining a plurality of pump chambers by the rotor, the vanes and the cam rings; and

a pressure plate arranged in the pump element storage part, with the driving shaft being inserted through a drive shaft insertion hole of the pressure plate in an axial direction along the rotation axis of the rotor, and having a rotor-side surface facing the rotor and the cam ring and a pressure receiving surface opposite the rotor-side surface,

the pressure plate defining a discharge hole extending therethrough in the axial direction and open to a discharge area in which the pump chambers decrease in volume with rotation of the rotor,

the pump housing defining: a suction hole open to a suction area in which the pump chambers increase in volume with rotation of the rotor; a suction passage connecting the suction port to the fluid reservoir; a high-pressure chamber located at a position facing the pressure receiving surface of the pressure plate and adapted to allow introduction of a discharge pressure thereto through the discharge port and bias the pressure plate toward the rotor and the cam ring by the action of the discharge pressure; and a low-pressure chamber located at a position corresponding to the suction area in the circumferential direction and adapted to allow introduction of a suction pressure thereto, and

the variable displacement vane pump further comprising:

an annular first seal member disposed on the pressure receiving surface of the pressure plate so as to surround the drive shaft insertion hole and separate the drive shaft insertion hole from the high-pressure chamber; and

an annular second seal member disposed on the pressure receiving surface of the pressure plate so as to surround the suction area and separate the suction area from the high-pressure chamber and the drive shaft insertion hole.

According to another aspect of the present invention, there is provided

variable displacement vane pump for supplying a hydraulic fluid from a fluid reservoir, comprising:

a pump housing provided with a pump element storage part;

a drive shaft supported rotatably in the pump housing and driven by an engine of a vehicle;

a pump element placed in the pump element storage part, the pump element comprising: a rotor rotated by the drive shaft and having a plurality of slots formed at positions in a circumferential direction around a rotation axis of the rotor; and a plurality of vanes retractably mounted in the respective slots;

an annular cam ring disposed movably around the pump element in the pump element storage part, thereby defining a plurality of pump chambers by the rotor, the vanes and the cam ring; and

a pressure plate arranged in the pump element storage part, with the drive shaft being inserted through a drive shaft insertion hole of the pressure plate in an axial direction along the rotation axis of the rotor, and having a rotor-side surface facing the rotor and the cam ring and a pressure receiving surface opposite the rotor-side surface,

the pressure plate defining a discharge hole extending therethrough in the axial direction at a position vertically above the drive shaft and open to a discharge area in which the pump chambers decrease in volume with rotation of the rotor,

the pump housing defining: a suction hole extending at a position vertically below the drive shaft and open to a suction area in which the pump chambers increase in volume with rotation of the rotor; a suction passage connecting the suction port to the fluid reservoir; a high-pressure chamber located at a position facing the pressure receiving surface of the pressure plate and adapted to allow introduction of a discharge pressure thereto through the discharge port and bias the pressure plate toward the rotor and the cam ring by the action of the discharge pressure; and a low-pressure chamber located at a position corresponding to the suction area in the circumferential direction and adapted to allow introduction of a suction pressure thereto, and

the variable displacement vane pump further comprising:

an annular drive-shaft-side seal member disposed on the pressure receiving surface of the pressure plate so as to surround the drive shaft insertion hole and separate the drive shaft insertion hole from the high-pressure chamber; and

an annular low-pressure-chamber-side seal member disposed on the pressure receiving surface of the pressure plate so as to surround the suction area and separate the suction area from the high-pressure chamber and the drive shaft insertion hole.

In the present invention, the low-pressure chamber side (suction area) of the variable displacement vane pump and the bearing part of the pump housing are separated from each other by the first and second seal members. This eliminates the possibility of sucking up the hydraulic fluid or sucking in the outside air under a negative pressure during fluid suction operation. It is therefore possible in the present invention to effectively prevent poor lubrication of the drive shaft.

The other objects and features of the present invention will also become understood from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a variable displacement vane pump according to a first embodiment of the present invention.

FIG. 2 is a cross section view of the variable displacement pump taken along line A-A of FIG. 1.

FIG. 3 is a cross section view of the variable displacement pump taken along line B-B of FIG. 2.

FIG. 4 is a cross section view of the variable displacement pump taken along line C-C of FIG. 1.

FIG. 5 is a schematic view of a pump body of the variable displacement vane pump, as viewed from the side of a pump cover, according to the first embodiment of the present invention.

FIG. 6A is a schematic view of an assembly unit in which a first bearing is mounted to the pump body according to the first embodiment of the present invention.

FIG. 6B is a schematic view of an assembly unit in which a second bearing is mounted to the pump cover according to the first embodiment of the present invention.

FIG. 7 is a schematic view of a variable displacement vane pump according to a modification of the first embodiment of the present invention.

FIG. 8 is a schematic view of a variable displacement vane pump according to a second embodiment of the present invention.

DESCRIPTIONS OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. Each of the following embodiments specifically refer to a variable displacement vane pump for supplying a hydraulic fluid from an oil pan (as a fluid reservoir) to an automatic transmission (such as CVT) of a vehicle.

First Embodiment

FIGS. 1 to 5, 6A and 6B show the structure of the variable displacement vane pump (occasionally simply referred to as “pump”) according to the first embodiment of the present invention.

As shown in FIGS. 1 to 3, the variable displacement vane pump of the first embodiment includes a pump housing 11, a drive shaft 12, an adapter ring 13, a cam ring 14, a pump element with a rotor 21 and a plurality of vanes 22, a pressure plate 23 and a control valve 50. Hereinafter, the terms “axial direction” and “circumferential direction” refer to directions along and around a rotation axis Q of the rotor 21, respectively, for explanation purposes.

The pump housing 11 is formed in a substantially cylindrical shape with a pump element storage part 10 and aligned in the axial direction. In the first embodiment, the pump housing 11 consists of two separate pieces: a substantially bottomed cylindrical-shaped (cup-shaped) pump body 15 as a first housing body having a cylindrical portion 10 a and an end wall (bottom) portion 10 b formed integral with the cylindrical portion 10 a and closing one end of the cylindrical portion 11 a and a pump cover 16 as a second housing body closing the other end of the cylindrical portion 10 b. A plurality of fixing parts 15 a and 16 a are formed in outer circumferences of the pump body 15 and the pump cover 16, respectively. The pump body 15 and the pump cover 16 are fixed to each other by insertion of a plurality of bolts 20 into the fixing parts 15 a and 16 a.

The drive shaft 12 is inserted and supported axially and rotatably in the pump housing 11 and is driven by a driving force transmitted from an engine of the vehicle.

The adapter ring 13 is formed in an annular shape and fitted in a circumferential wall of the pump element storage part 10. A circular-arc engagement groove is cut in an upper inner circumferential surface of the adapter ring 13.

The cam ring 14 is formed of a sintered iron-based metal material in an annular shape and disposed eccentrically movably in the adapter ring 13. A circular-arc cross-section engagement groove is cut in an outer circumferential surface of the cam ring 14.

A pin member 17 is engaged in the engagement grooves of the adapter ring 13 and the cam ring 14. A seal member 18 is retained on the inner circumferential surface of the adapter ring 13 at a position substantially radially opposite from the pin member 17. There are first and second hydraulic pressure chambers P1 and P2 defined by the pin member 17 and the seal member 18 in a radial space between the adapter ring 13 and the cam ring 14. By engagement of the pin member 17 in the engagement groove of the cam ring 14, the cam ring 14 is supported so as to swing eccentrically relative to the rotation center Q of the rotor 21 in a direction toward the first hydraulic pressure chamber P1 or the second hydraulic pressure chamber P2. A coil spring 19 is arranged in the second hydraulic pressure chamber P2 so as to bias the cam ring 14 all the time in the direction toward the first fluid pressure chamber P1, i.e., in the direction that the amount of eccentricity of the cam ring 14 relative to the rotation center Q of the rotor 21 (simply referred to as “eccentricity amount”) becomes maximum. The swinging movement of the cam ring 14 (i.e., the eccentricity amount of the cam ring 14) can be controlled under the hydraulic pressure control of the hydraulic pressure chambers P1 and P2 by the control valve 50 and under the biasing force of the coil spring 19 as will be explained later.

The pressure plate 23 is substantially disk-shaped and arranged in an end region of the pump element storage part 10 adjacent to the end wall portion 10 b so as to face the pump element (rotor 21) and the cam ring 14 in the axial direction.

The pump element is placed in the pump element storage part 10 and held between the pressure plate 23 and the pump cover 16. The pump element performs its pumping function when driven by the drive shaft 12 in a counterclockwise direction of FIG. 3. As mentioned above, the pump element is constituted by the rotor 21 and the vanes 22. The rotor 21 is coupled to an outer circumference of the drive shaft 12 by means of splines so as to rotate together with the drive shaft 12. A plurality of axial slots 21 a are cut in an outer circumference of the rotor 21 so as to extend at positions in the circumferential direction. The vanes 22 are rectangular plate-shaped and mounted retractably in the respective slots 21 a.

Substantially circular cross-section back pressure grooves are axially formed in the rotor 21 at positions adjacent to radially inner ends of the respective slots 21 a. Back pressure chambers 24 are defined by the back pressure grooves and radially inner ends of the vanes 22, respectively. By the action of the inner pressures of the back pressure chambers 24 and the centrifugal force of the rotation of the rotor 21, the vanes 22 project from the respective slots 21 a so that radially outer ends of the vanes 22 are held in sliding contact with an inner circumferential surface of the cam ring 14 all the time. There are thus a plurality of pump chambers 30 defined by respective pairs of the adjacent vanes 22, the pressure plate 23 and the pump cover 16 in a radial space between the cam ring 14 and the rotor 21. The volumes of the pump chambers 30 can be changed according to the eccentricity amount of the cam ring 14.

In an area where the volumes of the pump chambers 30 gradually increase by the rotation of the rotor 21 (referred to as “suction area”), a pair of circular arc groove-shaped first and second suction ports 25 a and 25 b are circumferentially cut in a plate surface of the pressure plate 23 facing the rotor 21 and the cam ring 14 (referred to as “rotor-side surface”) and in an inner surface of the pump cover 16, respectively, as shown in FIGS. 2 and 4. A suction hole 26 is formed through the pressure plate 23 in the axial direction at a predetermined circumferential position. A first low-pressure chamber 27 a is formed in an inner surface of the end wall portion 10 b of the pump body 15. On the other hand, a second low-pressure chamber 27 b is formed in the inner surface of the pump cover 16. A suction hole 29 is also formed in the inner surface of the pump cover 16 at a position vertically below the drive shaft 12. Further, a suction hole 28 is formed through the cylindrical portion 10 a of the pump body 15 and open to the outside of the pump housing 11. The first suction port 25 a is connected to and in communication with the suction hole 28 via the suction hole 26 and the first low-pressure chamber 27 a. The second suction port 25 b is connected to the suction hole 28 via the second low-pressure chamber 27 b and the suction hole 29. Thus, the low-pressure chamber 27 a, 27 b and the suction hole 26, 29, 38 constitute a continuous fluid suction passage from the suction port 25 a, 25 b to the outside of the pump housing 11. The hydraulic fluid is sucked from the oil pan through the suction hole 28 and introduced to the suction ports 25 a and 25 b as indicated by arrows in FIG. 4.

In an area where the inner volumes of the pump chambers 30 gradually decrease by the rotation of the rotor 21 (referred to as “discharge area”), a pair of circular arc groove-shaped first and second discharge ports 31 a and 31 b are circumferentially cut in the rotor-side surface of the pressure plate 23 and in the inner surface of the pump cover 16 at positions substantially axially symmetric with respect to the first and second suction ports 25 a and 25 b as shown in FIGS. 2 and 5. A circular arc groove-shaped high-pressure chamber 33 is formed in the inner surface of the end wall portion 10 b of the pump body 15. A discharge hole 32 is formed through the pressure plate 23 in the axial direction at a predetermined circumferential position vertically above the drive shaft 12. Although not specifically shown in the drawings, a fluid discharge passage is formed in the pump body 15. The first discharge port 31 a is connected to and in communication with the high-pressure chamber 33 via the discharge hole 32. The hydraulic fluid is fed from the discharge port 31 a to the high-pressure chamber 33 through the discharge hole 32. By the introduction of the discharge pressure into the high-pressure chamber 33, the pressure plate 23 is biased toward the rotor 21 and the cam ring 14. The hydraulic fluid is discharged from the high-pressure chamber 33 to the outside of the pump housing 11 (i.e., to the automatic transmission) through the fluid discharge passage.

As shown in FIG. 2, a drive shaft insertion hole 34 is formed through the center of the pressure plate 23. First and second shaft holes 35 a and 35 b are formed through the center of the end wall portion 10 a of the pump body 15 and through the center of the pump cover 16, respectively, as shown in FIGS. 2, 6A and 6B. Both of the first and second shaft holes 35 a and 35 b have an inner diameter slightly larger than an outer diameter of the drive shaft 12. The drive shaft 12 is inserted through the drive shaft insertion hole 34 and through the first and second shaft holes 35 a and 35 b. A first bearing B1 and a second bearing B2 are disposed in clearances between the first shaft hole 35 a and the drive shaft 12 and between the second shaft hole 35 b and the drive shaft 12, respectively. In the first embodiment, each of these bearings B1 and B2 is in the form of a plane bearing. As the hydraulic fluid is supplied to the clearances between the drive shaft 12 and the shaft holes 35 a and 35 b, the bearings B1 and B2 are lubricated with the hydraulic fluid.

Helical grooves 36 are cut in inner circumferential surfaces of the bearings B1 and B2. A fluid drain passage 37 is formed through the pump body 15 so as to provide communication from an outer end portion of the first shaft hole 35 a to the outside of the pump housing 11. By sliding contact (relative rotation) of the drive shaft 12 with the bearings B1 and B2, the hydraulic fluid leaked to the vicinity of the drive shaft 12 in the shaft holes 35 a and 35 b is fed through the helical grooves 36 and drained to the outside of the pump through the fluid drain passage 37. In the first embodiment, the fluid drain passage 37 is inclined vertically downward from the outer end portion of the first shaft hole 35 a (i.e. an outer end of the fluid drain passage 37 is situated vertically below an inner end of the fluid drain passage 37).

As shown in FIG. 2, circular arc groove-shaped first and second back pressure ports 38 a and 38 b are cut in the rotor-side surface of the pressure plate 23 and in the inner surface of the pump cover 16 at predetermined circumferential positions in the discharge area and facing the back pressure chambers 24. By the discharge of the hydraulic fluid from the high-pressure chamber 33, the discharge pressure is introduced to the first back pressure port 38 a through an introduction hole (not shown) and then to the second back pressure port 38 b through the back pressure chambers 24.

A circular arc lubrication groove 39 is cut in the inner surface of the pump cover 16 at a predetermined circumferential position located in the suction area and facing the back pressure chambers 24 of the rotor 21. The discharge pressure is also introduced to the lubrication groove 39 through the back pressure chambers 24 for lubrication of the sliding interface of the rotor 21 a.

Further, a first seal member S1 as a drive-shaft-side seal member and a second seal member S2 as a low-pressure-chamber-side seal member are disposed on a plate surface of the pressure plate 23 opposite the rotor-side surface (referred to as “pressure receiving surface”) so as to interrupt communication of the high-pressure chamber 33 with the drive shaft insertion hole 34 (first shaft hole 35 a) and communication of the low-pressure chamber 27 a (suction area) with the high-pressure chamber 33 and the drive shaft insertion hole 34 (first shaft hole 35 a) in the first embodiment.

More specifically, first and second seal grooves 41 and 42 are cut in the inner surface of the end wall portion 10 b of the pump body 15 as shown in FIGS. 2 and 5. The first seal groove 41 is formed in an annular shape at a position around the first shaft hole 35 a, whereas the second seal groove 42 is formed in an elongated/deformed annular shape at a position around the first low-pressure 27 a. These seal grooves 41 and 42 are partitioned by a partition wall 43. The first seal member S1 is formed corresponding in shape to the first seal groove 41 and is fitted in the first seal groove 41 so that the first shaft hole 35 a and the first low-pressure chamber 27 a, each of which is relatively low in pressure, are separated from the high-pressure chamber 33 by the first seal member S1. The second seal member S2 is formed corresponding in shape to the second seal groove 42 and is fitted in the second seal groove 42 so that the first shaft hole 35 a, which is in direct communication with the outside of the pump housing 11, is separated by the second seal member S2 from the first low-pressure chamber 27 a.

Furthermore, a high-pressure introduction groove 40 is formed in the pump body 15 at a position between the seal members S1 and S2 as shown in FIG. 5 such that the discharge pressure is introduced to the high-pressure introduction groove 40.

The control valve 50 is configured to control the amount of the hydraulic fluid discharged per one turn of the pump element (called “inherent discharge amount”) by changing the eccentricity amount of the cam ring 14. As shown in FIG. 3, the control valve 50 generally includes a spool valve body 52 slidably mounted in a valve hole 51 of the pump body 15, a plug 53 closing one end of the valve hole 51, a valve spring 54 disposed between the spool valve body 52 and the plug 53 so as to bias the spool valve body 52 toward the other end of the valve hole 51 and a solenoid 55 closing the other end of the valve hole 51 and having a push rod coupled to the spool valve body 52.

First and second land portions 52 a and 52 b are formed on an outer circumference of the spool valve body 52. By the first land portion 52 a, a first control pressure chamber R1 is defined adjacent to the solenoid 55 so that the hydraulic pressure upstream of a metering orifice (not shown) of the control valve 50 is introduced as the discharge pressure to the first control pressure chamber R1. By the second land portion 52 b, a second control pressure chamber R2 is defined adjacent to the plug 53 so that the hydraulic pressure downstream of the metering orifice is introduced to the second control pressure chamber R2. The axial position of the spool valve body 52 is controlled by the action of the pressure difference between the upstream and downstream of the metering orifice and the biasing force of the valve spring 54, thereby changing the eccentricity amount of the cam ring 14. Further, a low-pressure chamber R0 is defined between the land portions 52 a and 52 b. As the low-pressure chamber R0 is in communication with the outside of the pump housing 11 via a communication hole (not shown), the pressure of the low-pressure chamber R0 is maintained at a low pressure level equivalent to the suction pressure.

When the pressure difference between the first and second control pressure chambers R1 and R2 is relatively small, the spool valve body 52 is arranged adjacent to the solenoid 55 so as to allow communication between the first control pressure chamber R1 and the low-pressure chamber R0 via a first communication channel 56 a and allow communication between the second control pressure chamber R2 and the second hydraulic pressure chamber P2 via a second communication channel 56 b. As a result, the cam ring 14 is controlled to its maximum eccentric position under the hydraulic pressure of the second hydraulic pressure chamber P2 and the biasing force of the coil spring 19 whereby the discharge flow rate of the pump becomes maximum.

As the pressure difference between the first and second control pressure chambers R1 and R2 is increased, the spool valve body 52 is shifted toward the plug 53 against the biasing force of the valve spring 54 so as to allow communication between the first control pressure chamber R1 and the first hydraulic pressure chamber P1 via the first communication channel 56 a and allow communication between the second control pressure chamber R2 and the low-pressure chamber R0 via the second communication channel 56 b. As a result, the cam ring 14 is controlled in the direction that decreases its eccentricity amount by the hydraulic pressure of the first hydraulic pressure chamber P1 against the biasing force of the coil spring 19 whereby the discharge flow rate of the pump becomes decreased.

The operation and effects of the above-structured variable displacement vane pump will be explained below in detail.

For use as a hydraulic pressure source (oil pump) in the automatic transmission, the variable displacement vane pump is mounted to the inside of the automatic transmission. In this mounted state, the inside (pump element storage part 10) and outside of the pump housing 11 are in communication with each other via first and second radial clearances C1 and C2 between the drive shaft 12 and the bearings B1 and B2 of the pump housing 11.

In the conventional art, there is a problem that the hydraulic fluid in the first radial clearance C1 is sucked up to the suction side (i.e., to the first suction port 25 a), or the outside air is sucked in, through an axial clearance C3 between the pressure receiving surface of the pressure plate 23 and the inner surface of the end wall portion 10 b of the pump body 15 when the drive shaft insertion hole 34 becomes negative in pressure with increase in the negative pressure of the low-pressure chamber 27 a during fluid suction operation of the pump. This results in poor lubrication of the sliding interface between the drive shaft 12 and the bearing B1 in the bearing part (first shaft hole 35 a) of the pump housing 11.

In the first embodiment, by contrast, the vicinity of the first shaft hole 35 (i.e., the drive shaft insertion hole 34) and the vicinity of the low-pressure chamber 27 a are separated from each other by the first and second seal members S1 and S2. Even when there is generated a negative pressure during fluid suction operation of the pump, such a negative pressure is interrupted by these first and second seal members S1 and S2 (in particular, the second seal member S2). It is therefore possible to effectively avoid suck-up of the hydraulic fluid from the first radial clearance C1 to the suction side and suck-in of the outside air and prevent poor lubrication of the sliding interface between the drive shaft 12 and the bearing S1.

It is herein conceivable to provide a seal member between the pump housing 11 and the drive shaft 12 for the purpose of preventing leakage of the hydraulic fluid from the pump element storage part 10 to the outside of the pump housing 11. In the first embodiment, however, there is no seal member provided between the pump housing 11 and the drive shaft 12. It is thus possible in the first embodiment to reduce the parts count of the pump and improve the productivity and cost performance of the pump as compared to the case where the seal member is provided between the pump housing 11 and the drive shaft 12.

As the first and second seal members S1 and S2 are formed as separate pieces and held in the different seal grooves 41 and 42, it is possible to simplify the respective configurations of the seal members S1 and S2 and improve the holding of the seal members S1 and S2.

Further, the high-pressure introduction groove 40 is formed in the pump housing 11 in the low-pressure region surrounded by the seal members S1 and S2 in the first embodiment. As the discharge pressure is introduced to the high-pressure introduction groove 40 so as to compensate for insufficiency of the pressing force of the pressure plate 23 in the low-pressure region, it is possible to prevent deformation of the pressure plate 23.

In the first embodiment, the fluid drain passage 37 is formed in the pump housing 11 so that the hydraulic fluid leaked to the vicinity of the drive shaft 12 in the first shaft hole 35 a is drained to the outside of the pump housing 11 through the fluid drain passage 37 in the first embodiment. As the first shaft hole 35 a is in direct communication with the outside of the pump housing 11 via the fluid drain passage 37, it is possible in the first embodiment to effectively restrict the application of the negative pressure to the radial clearance C1 around the drive shaft 12 as compared the case where the hydraulic fluid leaked from the respective pump chambers 30 is recirculated to the suction side.

As the fluid drain passage 37 is inclined vertically downward from the first shaft hole 35 a so that the outer end of the fluid drain passage 37 is situated vertically below the inner end of the fluid drain passage 37, the outer end of the fluid drain passage 37 can be readily immersed in the hydraulic fluid within the oil pan. It is thus possible to avoid suck-in of the outside air through the fluid drain passage 37 and improve not only the efficiency of the pump but also the ability of the pump to discharge contaminants from the hydraulic fluid.

In addition, the suction hole 28 is formed in the cylindrical portion 10 a of the pump body 15 in the first embodiment. It is thus possible in the first embodiment to secure a relatively wide opening area of the suction hole 28 and improve the suction efficiency of the pump as compared to the case where the suction hole 28 is formed in the pump cover 16.

In the first embodiment, the low-pressure chambers 27 a and 27 b are brought into communication with the suction area from both sides in the axial direction; and the lubrication groove 39 is formed in the pump housing 11 at the predetermined circumferential position opposite the pressure plate 23 with respect to the rotor 21 and facing the rotor 21 on the inner circumferential side of the low-pressure chamber 27 b. As the discharge pressure is also introduced into the lubrication groove 39 so as to interrupt the negative pressure of the low-pressure chamber 27 b, it is possible to prevent the negative pressure of the low-pressure chamber 27 b from being exerted on the radial clearance C2 around the drive shaft 12.

Moreover, the plane bearing is used as bearing B1, B2 and disposed around the drive shaft 12; and the helical grooves 36 are cut in the inner circumferential surfaces of the bearings B1 and B2 so that the hydraulic fluid in the first and second radial clearances C1 and C2 is fed away from the pump element storage part 10 and positively discharged to the outside of the pump housing 11 by the sliding contact of the drive shaft 12 with the bearings B1 and B2 in the first embodiment. It is thus possible in the first embodiment to more effectively avoid suck-up of the hydraulic fluid to the suction side and suck-in of the outside air under the negative pressure during fluid suction operation.

[Modification]

FIG. 7 shows a modification example of the first embodiment. In the present modification example, the first seal groove 41 is formed to secure a relatively large circumferential area in the discharge area, i.e., provide a low-pressure region increasing portion 44 on the edge of the first shaft hole 35. The circumferential size of the low-pressure region in the discharge area is increased by the low-pressure region-increasing portion 44. Namely, the size of the low-pressure region in the circumferential direction is made larger in the discharge area than in the suction area. It is thus possible in the discharge area to reduce the pressing force of the pressure plate 23 caused by the discharge pressure in the axial clearance C3 and prevent the pressure plate 23 from being deformed by its excessive pressing force.

Second Embodiment

FIG. 8 shows the variable displacement vane pump according to the second embodiment of the present invention. The second embodiment is different from the first embodiment in that: there is no partition wall 43 on the pump body 15; the first and second seal grooves 41 and 42 are formed continuously at adjacent parts thereof with each other and thereby provided as one continuous seal groove 45; and the first and second seal members S1 and S2 are formed integral with each other and thereby provided as one seal member S0.

In the second embodiment, the seal groove 45 is integrally and continuously formed so as to save the space of the partition wall 43 as compared to the first embodiment where the partition wall 43 is formed on the pump body 15. It is thus possible to increase the opening area of the first suction port 24 a and improve the suction efficiency of the pump.

Further, the seal member S0 is formed integrally in place of the separate seal members S1 and S2 in the second embodiment. It is thus possible to reduce the parts count of the pump and improve the productivity of the pump.

Although the present invention has been described with reference to the above exemplary embodiments, the present invention is not limited to these exemplary embodiments. Various modification and variation of the embodiments described above will occur to those skilled in the art in light of the above teachings. For example, not only the configurations of the variable displacement vane pump not directly relevant to the features of the present invention (such as the positions of the suction ports 25 a and 25 b and the discharge ports 31 a and 31 b, the arrangements of the fluid suction and discharge passages, and the control method of the cam ring 14) but also the configurations of the variable displacement vane pump directly relevant to the features of present invention (such as the configurations of the seal grooves 41 and 42) can be modified as appropriate depending on the specifications of the engine to which the variable displacement vane pump is applied etc. without departing from the scope of the present invention.

The entire contents of Japanese Patent Application No. 2014-045815 (filed on Mar. 10, 2014) are herein incorporated by reference.

The scope of the present invention is defined with reference to the following claims. 

What is claimed is:
 1. A variable displacement vane pump for supplying a hydraulic fluid from a fluid reservoir, comprising: a pump housing provided with a pump element storage part; a drive shaft supported rotatably in the pump housing; a pump element placed in the pump element storage part, the pump element comprising: a rotor rotated by the drive shaft and having a plurality of slots formed therein at positions in a circumferential direction around a rotation axis of the rotor; and a plurality of vanes retractably mounted in the respective slots; an annular cam ring disposed movably around the pump element in the pump element storage part, thereby defining a plurality of pump chambers by the rotor, the vanes and the cam rings; and a pressure plate arranged in the pump element storage part, with the driving shaft being inserted through a drive shaft insertion hole of the pressure plate in an axial direction along the rotation axis of the rotor, and having a rotor-side surface facing the rotor and the cam ring and a pressure receiving surface opposite the rotor-side surface, the pressure plate defining a discharge hole extending therethrough in the axial direction and open to a discharge area in which the pump chambers decrease in volume with rotation of the rotor, the pump housing defining: a suction hole open to a suction area in which the pump chambers increase in volume with rotation of the rotor; a suction passage connecting the suction port to the fluid reservoir; a high-pressure chamber located at a position facing the pressure receiving surface of the pressure plate and adapted to allow introduction of a discharge pressure thereto through the discharge port and bias the pressure plate toward the rotor and the cam ring by the action of the discharge pressure; and a low-pressure chamber located at a position corresponding to the suction area in the circumferential direction and adapted to allow introduction of a suction pressure thereto, and the variable displacement vane pump further comprising: an annular first seal member disposed on the pressure receiving surface of the pressure plate so as to surround the drive shaft insertion hole and separate the drive shaft insertion hole from the high-pressure chamber; and an annular second seal member disposed on the pressure receiving surface of the pressure plate so as to surround the suction area and separate the suction area from the high-pressure chamber and the drive shaft insertion hole.
 2. The variable displacement vane pump according to claim 1, wherein the pump element storage part is in communication with the outside of the pump housing through a clearance between the pump housing and the drive shaft.
 3. The variable displacement vane pump according to claim 2, wherein the pump housing has a drain passage formed therein so as to allow therethrough the hydraulic fluid leaked to the vicinity of the drive shaft to be drained to the outside of the pump housing.
 4. The variable displacement vane pump according to claim 3, wherein an outer end of the fluid drain passage is situated vertically below an inner end of the fluid drain passage.
 5. The variable displacement vane pump according to claim 1, wherein the pump housing comprises: a first housing body having a cup shape including a cylindrical portion and a bottom portion formed integral with the cylindrical portion so as to close one end of the cylindrical portion; and a second housing body fixed to the first housing body so as to close the other end of the cylindrical portion; and wherein an outer end of the suction passage is open at the cylindrical portion of the first housing body.
 6. The variable displacement vane pump according to claim 1, wherein the suction passage is brought into communication with the suction area from both sides in the axial direction; and wherein the pump housing has a lubrication groove formed therein at a position opposite the pressure plate with respect to the rotor and facing the rotor so as to allow introduction of the discharge pressure thereto.
 7. The variable displacement vane pump according to claim 1, wherein the first and second seal members are formed as separate pieces.
 8. The variable displacement vane pump according to claim 7, wherein the pump housing has a high-pressure introduction groove formed therein at a position between the first and second seal members so as to allow introduction of the discharge pressure thereto.
 9. The variable displacement vane pump according to claim 7, wherein the pump housing has, formed therein, first and second seal grooves in which the first and second seal members are fitted, respectively.
 10. The variable displacement vane pump according to claim 7, wherein the pump housing has, formed therein, first and second seal grooves in which the first and second seal members are fitted, respectively; and wherein the first and second seal grooves are continuous at adjacent parts thereof with each other.
 11. The variable displacement vane pump according to claim 11, wherein the first and second seal members are formed integral with each other.
 12. The variable displacement vane pump according to claim 11, wherein the first seal member is formed such that the size of a low-pressure region between the first insertion hole and the drive shaft insertion hole in the circumferential direction is larger in the discharge area than in the suction area.
 13. The variable displacement vane pump according to claim 11, further comprises a plane bearing disposed around the drive shaft, wherein the plane bearing has a helical groove formed in an inner circumferential surface thereof so as to allow therethrough the hydraulic fluid between the plane bearing and the drive shaft to be fed away from the pump element storage part by relative rotation of the drive shaft and the plane bearing.
 14. A variable displacement vane pump for supplying a hydraulic fluid from a fluid reservoir, comprising: a pump housing provided with a pump element storage part; a drive shaft supported rotatably in the pump housing and driven by an engine of a vehicle; a pump element placed in the pump element storage part, the pump element comprising: a rotor rotated by the drive shaft and having a plurality of slots formed at positions in a circumferential direction around a rotation axis of the rotor; and a plurality of vanes retractably mounted in the respective slots; an annular cam ring disposed movably around the pump element in the pump element storage part, thereby defining a plurality of pump chambers by the rotor, the vanes and the cam ring; and a pressure plate arranged in the pump element storage part, with the drive shaft being inserted through a drive shaft insertion hole of the pressure plate in an axial direction along the rotation axis of the rotor, and having a rotor-side surface facing the rotor and the cam ring and a pressure receiving surface opposite the rotor-side surface, the pressure plate defining a discharge hole extending therethrough in the axial direction at a position vertically above the drive shaft and open to a discharge area in which the pump chambers decrease in volume with rotation of the rotor, the pump housing defining: a suction hole extending at a position vertically below the drive shaft and open to a suction area in which the pump chambers increase in volume with rotation of the rotor; a suction passage connecting the suction port to the fluid reservoir; a high-pressure chamber located at a position facing the pressure receiving surface of the pressure plate and adapted to allow introduction of a discharge pressure thereto through the discharge port and bias the pressure plate toward the rotor and the cam ring by the action of the discharge pressure; and a low-pressure chamber located at a position corresponding to the suction area in the circumferential direction and adapted to allow introduction of a suction pressure thereto, and the variable displacement vane pump further comprising: an annular drive-shaft-side seal member disposed on the pressure receiving surface of the pressure plate so as to surround the drive shaft insertion hole and separate the drive shaft insertion hole from the high-pressure chamber; and an annular low-pressure-chamber-side seal member disposed on the pressure receiving surface of the pressure plate so as to surround the suction area and separate the suction area from the high-pressure chamber and the drive shaft insertion hole.
 15. The variable displacement vane pump according to claim 14, wherein the pump element storage part is in communication with the outside of the pump housing through a clearance between the pump housing and the drive shaft.
 16. The variable displacement vane pump according to claim 15, wherein the pump housing has a drain passage formed therein so as to allow therethrough the hydraulic fluid leaked to the vicinity of the drive shaft to be drained to the outside of the pump housing.
 17. The variable displacement vane pump according to claim 16, wherein an outer end of the fluid drain passage is situated vertically below an inner end of the fluid drain passage.
 18. The variable displacement vane pump according to claim 14, wherein the pump housing comprises: a first housing body having a cup shape including a cylindrical portion and a bottom portion formed integral with the cylindrical portion so as to close one end of the cylindrical portion; and a second housing body fixed to the first housing body so as to close the other end of the cylindrical portion; and wherein an outer end of the suction passage is open at the cylindrical portion of the first housing body.
 19. The variable displacement vane pump according to claim 14, wherein the suction passage is brought into communication with the suction area from both sides in the axial direction; and wherein the pump housing has a lubrication groove formed therein at a position opposite the pressure plate with respect to the rotor and facing the rotor so as to allow introduction of the discharge pressure thereto.
 20. The variable displacement vane pump according to claim 14, wherein the drive-shaft-side seal member and the low-pressure-chamber-side seal member are formed as separate pieces. 